Conventional processes for moisture removal from minerals such as coal include screening, centrifugation and vacuum filtration. In the case of coal products, it is economically important to reduce the moisture content prior to land transport of the particulate mass as transport costs are essentially according to weight and it is an economic penalty to transport as much as 10% of the weight of the product as unwanted water. Furthermore in some industrial processes using coal products, such as power generation, it is a substantial thermal penalty to have a significant level of moisture in the coal as energy in burning the coal is then utilised in driving off the moisture as steam.
For many years, it has been conventional to use centrifuges to reduce moisture levels to around 6 to 8 wt % where the particle size range is typically less than 30 mm and greater than 0.5 mm. With conventional practice, practical limit for dewatering is controlled by the relative opposing magnitudes of capillary forces causing the water to be retained in the particulate mass and the applied forces attempting to strip the water from the mass.